Effect of Printing Orientation and Postcuring Time on the Flexural Strength of 3D-Printed Resins

Purpose To evaluate the effect of printing orientation combined with different postcuring times on the flexural strength of 3D-printed resins. Materials and methods A total of 480 rectangular specimens with the dimensions of 64x10x3.3 mm were designed and fabricated from two 3D-printed acrylic resins and one heat-polymerized resin (HP). 3D-printed groups were divided into 3 groups according to printing orientations (0-, 45-, 90-degree); each group was subdivided into 4 groups according to postcuring time (30, 60, 90, 120 min.). All specimens were subjected to thermal cycling (10,000 cycles) before testing flexural strength. Fractured surfaces were examined under a scanning electron microscope (SEM). ANOVA and Tukey's post hoc tests were used for data analysis (alpha = 0.05). Results The result of this study showed that the highest flexural strength values of 3D-printed resin (NextDent, and ASIGA) were in 0-degree groups. Also, the flexural strength values increased when postcuring time was increased, regardless of the printing orientation; the highest flexural strength was recorded at 120 minutes postcuring time in all orientations. SEM analysis showed a rougher surface with irregular lamellae which represented a ductile fracture confirming that high energy is required for crack propagation and these features markedly increased as postcuring time increased. Conclusion The results showed that the 0-degree orientation groups showed higher flexural strength compared to other groups. Similarly, with increased postcuring time, the flexural strength increased.